This invention relates to access systems as used in wireline telephony, and, more specifically, to a switch proxy for use in conjunction with an access system remote terminal to route telephone calls when communications between a remote terminal of an access system and its controlling switching system is lost.
Wireline telephone service providers use access systems (such as, but not limited to, subscriber loop carriers and digital loop carriers) to serve telephone subscribers that are not economically or practically served directly from the nearest local switching system. An access system consists of a remote terminal that is connected to a local switching system by one or more digital trunk groups. These trunk groups contain a multiplicity of digital channels for carrying the voice traffic and separate digital channels for control information between the switching system and the remote terminal. The local switching system controls the remote terminal as if it were an extension of the switching system. In the usual case, a remote terminal provides digital connectivity between the remote telephone subscribers and the host switching system and does not participate in the routing of calls. In this manner, service providers are afforded more options in providing telephone service to subscribers; in particular, these access systems provide a much more economical approach to serve a small remote community of subscribers than the use of expensive local switching systems or proprietary remote switching modules.
The simplicity of aggregating all of the call control functionality in the host switching system creates a problem in the art. That is, when the host switching system is unable to communicate with the remote terminal, either through failure of components of the digital trunks or of the switching system itself, subscribers served by the remote terminal no longer have any telephone service. Even though the connectivity with the greater network is lost and the remote terminal may be otherwise fully functional, the subscribers terminated on this remote system still cannot communicate with one another. The severity of this problem may be confounded by the fact that these subscribers are frequently served by this technology precisely because they are remote; these remote settings necessitate the use of local emergency responders and limit other communications options (e.g, cellular telephony). Therefore, the ability to continue to locally switch calls between subscribers served by remote systems that have lost communications with a host switching system is an important public safety consideration.
While manufacturers of access systems are currently considering the incorporation of so-called “emergency stand alone” service into their next generation of product, this does nothing to address the provision of this capability to the vast majority of access systems which are currently in use and are otherwise fit for service. Other suggestions in the art pertain to installation of a “miniature” switching system in the proximity of the remote terminal to serve as a local host. This approach is not only expensive but impractical on several counts:                i) it changes the basic architecture of the exchange network,        ii) it increases the number of switches to administer and maintain,        iii) it actually increases the probability of a service outage by putting another switching system into the chain, and        iv) these remote terminals are frequently installed in field cabinets where it may be impossible to install an additional complex system.Thus there currently does not exist an economical or practical scheme for providing emergency stand alone service to subscribers served by the installed base of access systems.        